The GOP debate is tonight! Here's what you need to know

Donald Trump at a rally in Dallas, Texas. AP Summer has (unofficially) turned to fall, and the presidential campaign is kicking into full gear.

The second Republican presidential primary debate will take place Wednesday night in Simi Valley, California, where 11 candidates will square off on the main debate stage.

CNN, which is hosting the second debate, originally said it would limit the main-stage participants to 10, like Fox News did last month.

But the network changed its debate criteria to make room for former Hewlett Packard CEO Carly Fiorina, who surged following a strong performance in last month's so-called happy hour, lower-tier debate.

The remaining four Republican contenders who didn't qualify for the main debate, meanwhile, will participate in a separate debate. All will look to stand out amid an increasingly crowded field, and the continued behemoth that is Donald J. Trump.

The polling

According to Real Clear Politics' average of six recent national polls, here's a look at where the candidates stand going into Wednesday night. From the top tier:

Donald Trump, real-estate magnate: 29.8% average as of Wednesday (up from a 24.3% average before the August 6 debate)

Ben Carson, retired neurosurgeon: 17.8% (up from 5.8%)

Jeb Bush, former Florida governor: 7.8% (down from 12.5%)

Ted Cruz, US senator from Texas: 6.7% (up from 5.5%)

Marco Rubio, US senator from Florida: 5.8% (up from 5.3%)

Mike Huckabee, former Arkansas governor: 4.3% (down from 6.8%)

Carly Fiorina, former Hewlett Packard CEO: 4.3% (up from 1.3%)

Scott Walker, Wisconsin governor: 3.8% (down from 9.5%)

John Kasich, Ohio governor: 3.5% (up from 2.8%)

Rand Paul, US senator from Kentucky: 2.7% (down from 4.5%)

Chris Christie, New Jersey governor: 2.0% (down from 3.5%)

Republican 2016 presidential candidate Donald Trump talks with fellow candidate Jeb Bush during a commercial break at the first official Republican presidential candidates debate of the 2016 presidential campaign in Cleveland. Thomson Reuters

And the bottom tier:

Rick Santorum, former US senator from Pennsylvania: 1.0% (down from 1.3%)

What the campaigns are saying

Business Insider asked the campaigns of each of the 11 main-stage candidates of their goals for the second presidential debate, and if they planned to have their candidate engage with Trump. Here's how some responded.

Alex Conant, communications director for Marco Rubio:

"A couple of points:

- While other candidates are falling and need to mix things up tomorrow, Marco is confident in his strategy and our campaign is on track. Don't look for any big surprises from Marco tomorrow night.

- Marco had a terrific first debate in Cleveland, and he's approaching the second debate the same way.

- Marco hopes to talk about his ideas for a New American Century and why he believes Washington is stuck in the past."

- Anytime Marco is on TV speaking to millions of voters, it's a good night for our campaign."

John Weaver, top strategist to Ohio Gov. John Kasich:

"While we are still in the introductory stage, this debate offers another opportunity for Americans to meet Ohio Governor John Kasich, who is presidential in tone and conduct and also has the exclusive conservative policy depth on domestic and national security issues. He is prepared to build upon his positive performance in Cleveland and to stand out again on a crowded stage, despite what could be desperate chaos around him.

"We are prepared to engage other candidates as need be, especially if they launch a desperate attack as some have indicated, but primarily the focus will be on discussing how a positive, pro-growth agenda can include all Americans."

Doug Watts, communications director for Ben Carson:

"We would like to meet people's expectations of us, have a reasonable chance to share our vision and values, and be discussed around the water cooler the following day.

"We expect to engage with Mr. Trump in the same respectful, civil manner that we engage each and every one of our colleagues."

Sergio Gor, communications director for Rand Paul:

"Senator Paul will focus on highlighting his conservative credentials, his proposals for America and why he's best positioned to defeat a democrat in the general election. From our flat tax to proposing term limits, Senator Paul is a tested conservative who is able to grow the GOP tent and deliver a victory against Hillary Clinton. How Senator Paul engages other candidates will remain to be seen, but he won't fade quietly into the background on Wednesday night."

And two candidates in particular — Kasich and Fiorina — have surged in the past month after strong performances in August's debate. Can they repeat their performances and vault into clear top-tier candidates?